/*
 * Copyright 1999-2101 Alibaba Group.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.codefinger.json.util;

/**
 * for concurrent IdentityHashMap
 * 
 * @author wenshao[szujobs@hotmail.com]
 */
@SuppressWarnings("unchecked")
public class IdentityHashMap<K, V> {

	public static final int		DEFAULT_TABLE_SIZE	= 1024;

	private final Entry<K, V>[]	buckets;
	private final int			indexMask;

	public IdentityHashMap() {
		this(DEFAULT_TABLE_SIZE);
	}

	public IdentityHashMap(int tableSize) {
		this.indexMask = tableSize - 1;
		this.buckets = new Entry[tableSize];
	}

	public final V get(K key) {
		final int hash = System.identityHashCode(key);
		final int bucket = hash & indexMask;

		for (Entry<K, V> entry = buckets[bucket]; entry != null; entry = entry.next) {
			if (key == entry.key) {
				return entry.value;
			}
		}

		return null;
	}

	public boolean put(K key, V value) {
		final int hash = System.identityHashCode(key);
		final int bucket = hash & indexMask;

		for (Entry<K, V> entry = buckets[bucket]; entry != null; entry = entry.next) {
			if (key == entry.key) {
				entry.value = value;
				return true;
			}
		}

		Entry<K, V> entry = new Entry<K, V>(key, value, hash, buckets[bucket]);
		buckets[bucket] = entry; // 并发是处理时会可能导致缓存丢失，但不影响正确性

		return false;
	}

	public int size() {
		int size = 0;
		for (int i = 0; i < buckets.length; ++i) {
			for (Entry<K, V> entry = buckets[i]; entry != null; entry = entry.next) {
				size++;
			}
		}
		return size;
	}

	protected static final class Entry<K, V> {

		public final int			hashCode;
		public final K				key;
		public V					value;

		public final Entry<K, V>	next;

		public Entry(K key, V value, int hash, Entry<K, V> next) {
			this.key = key;
			this.value = value;
			this.next = next;
			this.hashCode = hash;
		}
	}

}
